Raman spectroscopy characterisation of oriented bundles of single-crystal rutile-phase TiO2 nanorods prepared by hydrothermal bath deposition on transparent conducting substrates

• Published in: Applied physics. A, Materials science & processing Materials science & processing, 2019-06, Vol.125 (6), p.1-10, Article 389
• Main Authors: Mbulanga, C. M., Erasmus, R. M., Urgessa, Z. N., Djiokap, S. R. Tankio, Olivier, E. J., Goosen, W. E., Botha, J. R., Betz, R.
• Format: Article
• Language: English
• Subjects: Applied physics; Bundles; Bundling; Characterization and Evaluation of Materials; Condensed Matter Physics; Crystal lattices; Crystal structure; Deposition; Grain boundaries; Lattice vibration; Machines; Manufacturing; Materials science; Morphology; Nanorods; Nanotechnology; Optical and Electronic Materials; Phonons; Physics; Physics and Astronomy; Processes; Raman spectra; Raman spectroscopy; Rutile; Single crystals; Spectrum analysis; Substrates; Surfaces and Interfaces; Thin Films; Tin dioxide; Titanium dioxide
• ISSN: 0947-8396; 1432-0630
• DOI: 10.1007/s00339-019-2688-4

Rutile-phase TiO 2 rods prepared by hydrothermal bath deposition on F:SnO 2 are in fact bundles of single-crystal TiO 2 prismatic nanorods of ~ 4 nm diameter each. These bundles of rutile-phase TiO 2 nanorods have tetragonal morphology and are strain-free (or the strain in all the samples is the same). Bundles of TiO 2 that are oriented tetragonally with respect to the substrate’s surface, can be prepared for optimized growth times. It is observed that bundles of TiO 2 nanorods act as single entities from the point of view of the Raman spectra (and thus lattice vibrations). Single prismatic nanorods of ~ 4 nm width, as observed via TEM, appear to act as “larger” crystals to the lattice phonons once stacked together to form large oriented bundles of TiO 2 . Hence, the phonon confinement effect cannot be observed because translational symmetry is preserved at the grain boundaries of the nanorods that make each TiO 2 bundle. Moreover, an increase in the density of bundles growing preferentially in the [002] direction, perpendicular to the substrate surface, results in an unusual increase of room and low (77 K) temperature Raman band E g / A 1g intensity ratios.